As a double-side pressure-sensitive tape which does not use a release paper (separator), a tape obtained by coating a support on one side with an acrylic pressure-sensitive adhesive and on the other side with a rubber-based pressure-sensitive adhesive is known so far. However, this has drawbacks that adherends to which this tape is applicable are limited, that the property of separating pressure-sensitive adhesives from each other after laminating is unequivocally determined by the modulus of elasticity or the like of the pressure-sensitive adhesives and cannot be varied, and further that since acrylic pressure-sensitive adhesives, for example, have poor storage stability, they are unusable in articles to be used over a long period of time. Further, acrylic pressure-sensitive adhesives and rubber-based pressure-sensitive adhesives differ considerably from each other in properties such as adhesive force, heat resistance, and solvent resistance, and use of the rubber-based pressure-sensitive adhesive is unsuitable in case of bonding with the pressure-sensitive tape, followed by heat treatment, resin processing, or long-term use.
Also, a tape is known as a double-side pressure-sensitive tape free from the necessity of a release paper, which is obtained by coating a support on one side with a pressure-sensitive adhesive prepared by partially crosslinking an acrylic resin having a carboxyl group in a side chain with an isocyanate and on the other side with a pressure-sensitive adhesive prepared by partially crosslinking an acrylic resin having a hydroxyl group in a side chain with a melamine resin (e.g., Unexamined Published Japanese Patent Application 54-108833). However, this tape has a drawback that since the main components of the pressure-sensitive adhesives are limited to acrylic resins, adherends are limited naturally and adhesion to adherends such as polyolefins is poor. Further, use of this tape in sanitary articles or the like has been not preferable since there is a fear that formalin may be emitted because of the crosslinking with a melamine resin.
The first object of the present invention, which has been attained to solve those problems, is to provide a double-side pressure-sensitive tape which is free from the necessity of use of a release paper and which, even when those tapes are laminated with each other, can be easily separated at the interface between pressure-sensitive adhesive layers, by using a pressure-sensitive adhesive layer having a specific composition on one side thereof.
On the other hand, known as a pressure-sensitive tape for use as a fastener tape for fixing the front part of a disposable diaper to the back part thereof is, as shown, for example, in FIG. 20 and FIG. 21, a pressure-sensitive tape 10 produced by double-folding a tape substrate 11 in a manner such that a near-one-end part 11a and a near-other-end part 11b of the substrate become faced to each other, forming a first pressure-sensitive adhesive layer 12 on an inner surface of the near-one-end part 11a in the tape substrate 11, on the other hand, forming a release layer 13 for the first pressure-sensitive adhesive layer 12 on an inner surface of the near-other-end part 11b in the tape substrate 11, and further forming a second pressure-sensitive adhesive layer 14 on an outer surface of the near-other-end part 11b in the tape substrate 11 (Unexamined Published Japanese Utility Model Application 61-94536).
That is, this pressure-sensitive tape 10 has been designed to be used in a manner such that the pressure-sensitive tape 10 is applied beforehand through the second pressure-sensitive adhesive layer 14 to the inner surface of a back part 5A1 in a diaper 5A, the diaper 5A is applied to a baby or infant, the near-one-end part 11a of the tape substrate 11 is peeled from the near-other-end part 11b, and this near-one-end part 11a is bonded to a center tape 5A3 disposed on a front part 5A2 of the diaper 5A, thereby fixing the back part 5A1 of the diaper 5A to the front part 5A2.
According to this pressure-sensitive tape, there is no need to separately dispose a release tape because the tape substrate 11 itself functions as a release tape for the first pressure-sensitive adhesive layer 12 and protects the first pressure-sensitive adhesive layer 12. The above pressure-sensitive tape, therefore, has an advantage that the production process can be simplified and the cost can be reduced.
However, in this pressure-sensitive tape 10, since the inner surface of the near-one-end part 11a in the tape substrate 11 is the only part where the first pressure-sensitive adhesive layer 12 can be formed, the area in which the tape substrate 11 is bonded to the center tape 5A3 is small. Because of this, there has been a problem that the fixing strength to the front part 5A2 of the diaper 5A is so low that the tape substrate 11 shifts as shown by the alternate long and short dash line in FIG. 22 if a tensile force is applied, according to the movement of the baby or infant wearing the diaper 5A, to the tape substrate 11 in a direction along the length of the substrate, and this not only loosens the diaper 5A but also is prone to cause rubefaction or a rash on the skin 5B of the baby or infant because the other end part in the tape substrate 11 contacts with the skin 5B of the baby or infant.
Although it is thought that the above problem may be solved by increasing the area of the first pressure-sensitive adhesive layer 12 by elongating the length size of the tape substrate 11, this results in an increase in the amount of a material used for producing the tape substrate 11 and, as a result, the effect of cost reduction brought about by unnecessity of a release paper is lost.
The second object of the present invention is to provide a pressure-sensitive tape which can markedly improve a fixing strength without increasing the area of the tape substrate.